Why is 08 or 09 in Python invalid? [duplicate]

Answer 1

In Python (along with many other C-origin languages), a leading 0 (and, increasingly a leading 0O) indicate that the number is octal, not decimal. See https://docs.python.org/2/reference/lexical_analysis.html#integer-and-long-integer-literals for details.

For example, and for kicks, see what 010 evaluates to.

Answer 2

A number with a leading zero is interpreted as octal literal. So 8 and 9 are invalid in octal. Only digits 0 to 7 are valid.

Try in interpreter:

>>> 011
9
>>> 012
10
>>> 013
11

Answer 3

If a number starts with 0, it means it's an octal number:

>>> 010
8